The present invention relates generally to a zoom lens, and more particularly to a zoom lens lending itself to a camera-specific taking lens.
In recent years, there have been growing demands for camera-specific zoom lenses capable of taking photographs both over an ever wider scene through zooming and at an ever wider range of subject distance from infinity to a short distance.
So far, focusing on subjects on short distances has generally been implemented by moving the whole or a part of one lens group among lens groups with the space between them varying at the time of zooming. However, this gives rise to large aberration fluctuations upon focusing that lead to degradations in association with short-distance photography, or is less than satisfactory in terms of much wider short-distance scenes. There has also been the so-called floating mechanism used with single-focus lenses, wherein multiple lens groups are independently moved upon focusing to make correction of aberration fluctuations at short distances, thereby achieving plenty of short-distance performance or the specifications for the shortest distance. For reasons of lens or mechanism size reductions, fast AF, and reductions in the shortest distance, the so-called inner focus mode wherein internal lens groups are driven for focusing goes mainstream for focusing with taking lenses. An example of the floating mechanism of the inner focus mode applied to zoom lenses is set forth in, for instance, Patent Publication 1.
Patent Publication 1
JP(A)2004-341060
A problem with the inner focus mode applied to a zoom lens is, however, that the floating mechanism combined with that gets a lot more complicated, because of changes depending on a zooming position in the amount of movement of a focusing lens group from infinity to a constant subject distance.